| Phyllostachys.rivalis H.R.Zhao naturally widely distributes in Fujian,Guangdong and Zhejiang provinces.It can grow and reproduce normally in flooded soil which suggestes its potential in application in vegetation restoration hydro-flutuation belt of lakes or rivers.However,the tolerance mechanism and its response to heavy metals stress of Ph.rivalisare rarely investigated.Hence,it is vital to explore the responses of Ph.rivalisto soil flooding and heavy metals and related mechanism,which can provide substantial information on assessing the potential in vegetation restoration application.In order to explore the tolerance mechanism to soil flooding,we examined 1)the biological characteristic of Ph.rivalis under different flooded conditions;2)the physiological and biochemical responses of Ph.rivalisto different flooding treatment;3)the physiologcal responses of Ph.rivalis to Cd and Pb in aquatic solution;and 4)the accumulation ability of Cd and Pb in Ph.rivalistissues.1 Biological characteristics of Ph.rivalisThe shooting of Ph.rivalis mainly occurred in the middle to the end of May.Ph.rivalis belongs tosympodial mixed bamboo species.The root and rhizome systems are flourishing,and the rhizome is short which enable its strong ability in shooting and expanding.There is a visible loop with dense stoma in phloem of rhizome can be clearly observed,which can be identified to the characteristic of submergence tolerant plant.After the continuous flooding for 360 d,the survival rateof Ph.rivalis were 83.33%、78.89%、60.00% and 0,corresponding to water level of 5、10、50 and 100 cm,respectively。2 Photosynthetic responses of leaf in Ph.rivalis to soil floodingThe light capture,energy transfer and utilization of leaf varied as affected by different flooding depth.The decreases of Pn in the early and middle stage of flooding can be ascribed to stomatal limitation,while the Pn decrease in the later stage of flooding due to non-stomatal limitation.The result suggested that Phylllostachys rivalis can maintain relatively high electron transport rate(ETR),photochemical quenching coefficient(qP)and the ration of absorbed light in photochemistry(P)values in the early stage of flooding,and enhance the non-photochemical quenching coefficient(qN)to regulate their energy metabolism,dissipate excess light energy via heat dissipation,thus alleviating the light photoinhibition and photooxidation.The continuous long~term soil flooding can damage the photosystem II(PSII)while showed insignificant adverse effect on functional center of PSII.The significant differences were observed among treatment I and treatment Ⅱ and CK(P<0.05).The effect of flooding on chlorophyll fluorescence parameters and energy dissipation was also obviously dependent to water level.3 The physiological responses in leaf and root system of Ph.rivalisThe antioxidant enzyme system,osmotic adjustment substances and endogenous hormones in leaves and roots of Ph.rivalis were all affected differently by different flooding treatments.The SOD activity was markedly decreased under flooding depth of 10 cm while exhibiting insignificant differences compared with that of the control under flooding depth of 5 cm.The activities of POD and CAT in the leaves and roots of Ph.rivalis were all higher than those of control,and decreased with the prolonged flooding period.The contents of osmotic adjustment substances including soluble protein and starch in the roots and leaves of Ph.rivalis were higher than those of control under the flooding depth of 5 cm,while they all showed opposite pattern under the flooding depth of 10 cm.Although the IAA content in leaves decreased with the prolonged flooding period,it was still higher than that of control.The ZR and GA contents in leaves were much lower than control,but the ABA content in roots was significantly higher than that of control.The relative membrane permeability and MDA content of leaves and roots were higher than those of control at both flooding depth.A significant water level effect was observed,ie,the flooding depth of 10 cm caused more serious membrane lipid peroxidation of leaves and roots than that of flooding depth of 5 cm.4 Nutrient element distribution patterns in Ph.rivalis modulesFlooding depth and duration significantly affected the C content in modules.The C content in leaves,branches,and roots increased significantly(P<0.05)than that of the control after 90 d of flooding.With prolonged flooding,the C content did not differ significantly from that of the control at 180 d,but decreased significantly at 360 d.Continuous flooding significantly affected the contents of N,P,K,Ca,Fe,and Mg in Ph.rivalis modules.The combined interactions among treatment time,flooding depth,and modules significantly affected the mineral element contents.At 90 d of flooding,the N,P,Ca,Fe,and Mg contents in leaves increased,whereas the N and P contents decreased significantly.All these elements in modules decreased significantly,except the elevated K,Fe,and Mg contents in roots at 180 and 360 d of flooding.The correlation coefficients of C-K,N-K,P-K,Fe-Ca,and Fe-Mg in I increased,which suggested the synergistic effect of mineral elements was enhanced at water depths of 5 cm,whereas those correlation coefficients decreased in II,implying a decreased synergistic effect with increased water depth to 10 cm.Soil flooding significantly increased the C/N and C/P in leaves than that of control(P<0.05),whereas N/P in leaves remained unaffected(P>0.05),suggesting a relatively high intrinsic stability of Ph.rivalis under flooding stress.5 The effect of Cd and Pb on physiological characteristics in leaf of Ph.rivalisThe Pn firstly increased then decreased while the values of Pmax、AQY、LCP、LSP、CUE and LUE all decreased with the elevated concentrations of solution Cd and Pb.Low concentrations of Cd(0.5mg·L-1)and Pb(150,300 mg·L-1)showed little effect on chlorophyll content,MDA and antioxidant enzymes,while high concentrations of Cd(30 mg·L-1)and Pb(1500mg·L-1)significantly decreased chlorophyll content.It suggested Cd and Pb inhibited the synthesis or enhanced the degradation of photosynthetic pigment.However,Ph.rivalis can adjust the ratio of Chla to Chlb thus maintaining the relative abundant reaction centre pigment.Low concentrations of Cd(0.5 mg·L-1)and Pb(150,300 mg·L-1)increased the activities of SOD、POD and CAT while showed little effect on MDA.The high concentrations of Cd(30 mg·L-1)and Pb(1500 mg·L-1)caused MDA double increased which suggested the high dose of Cd and Pb caused the accumulation of superoxide anion beyond the quenching capacity of antioxidant,thus leading to the membrane lipid peroxidization.The effects of Cd and Pb on the N,P and K accumulation in organs of Ph.rivalis were slightly different under soil flooding condition.Low Cd treatment(0.5 mg·L-1)effectively promoted the N,P and K accumulation in Ph.rivalis roots and branches,while showing no obvious effect on the N and P accumulation in bamboo rhizome,anddecreasing K content in rhizome,High Cd concentration(30 mg·L-1)decreased the content of N,P and K in different organs.The N,P and K contents were almost all increased in each organ under Pb treatment.Ph.rivalis can absorb more N,P and K to alleviate the toxic effects of Pb and Cd treatments under soil flooding condition,which implied the possible tolerance mechanism for Ph.rivalis to adapt to the stress of Pb and Cd in soil.6 The effect of Cd and Pb on nutrient element accumulation in Ph.rivalisThe Cd and Pb contents in each organ of Ph.rivalis gradually elevated with the increase of treatment concentration of heavy metals,which showed a dose effect.The Cd and Pb accumulation was mainly concentrated in root and rhizome of Ph.rivalis.The Cd and Pb distribution in subcellular structures of leaves and roots were different.The Cd mostly accumulated in the cell wall,followed by soluble solids,and only a small amount of Cddistributed in the cell.The Pb content in subcellular structures displayed in the order thatsolublesolid > cell wall > organelle.In short,Ph.rivaliscan maintain normal growth and regeneration when being exposed to soil flooding as watrer level less than 50 cm,which suggestPh.rivalis can tolerate long term soil flooding under 50 cm water level.Ph.rivalis can adjust the content of endogenous hormones and promote the accumulation of osmotic substances,further improving the ability of cell osmotic adjustment,alleviating the membrane lipid peroxidation damage caused by superoxide radical,and improving the adaptability of Ph.rivalis to flooding stress.The continuous flooding influenced the absorptioncapacity of mineral elements by Ph.rivalis roots,but promoted the acropetaltranslocation of mineral elements,which could maintain the C assimilation capacity and mineral element homeostasis of Ph.rivalis grown under continuous flooding stress.Ph.rivalis can also tolerate the stress of medium concentrations of Cd and Pb through maintaining relative high photosynthetic rate and activities of antioxidant enzymes under flooding conditions.Taken together,Ph.rivalis has great potential in application in vegetation restoration hydro-flutuation belt of lakes or rivers. |
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